Feature/fix vcvars filter known (#3941)

* before win

* added test

* Avoid empty path

conans/client/tools/win.py

@@ -457,9 +457,10 @@ def relevant_path(path):
             keywords = "msbuild", "visual", "microsoft", "/msvc/", "/vc/", "system32", "windows"
             return any(word in path for word in keywords)
 
-        path = new_env.get("PATH", "").split(";")
-        path = [entry for entry in path if relevant_path(entry)]
-        new_env["PATH"] = ";".join(path)
+        path_key = next((name for name in new_env.keys() if "path" == name.lower()), None)
+        if path_key:
+            path = [entry for entry in new_env.get(path_key, "") if relevant_path(entry)]
+            new_env[path_key] = ";".join(path)
 
     return new_env
 

conans/test/util/tools_test.py

@@ -801,6 +801,24 @@ def vcvars_env_not_duplicated_path_test(self):
                         # If the entry was already repeated before calling "tools.vcvars" we keep it
                         self.fail("The key '%s' has been repeated" % value)
 
+    @unittest.skipUnless(platform.system() == "Windows", "Requires Windows")
+    def vcvars_filter_known_paths_test(self):
+        settings = Settings.loads(default_settings_yml)
+        settings.os = "Windows"
+        settings.compiler = "Visual Studio"
+        settings.compiler.version = "15"
+        settings.arch = "x86"
+        settings.arch_build = "x86_64"
+        with tools.environment_append({"PATH": ["custom_path", "WindowsFake"]}):
+            tmp = tools.vcvars_dict(settings, only_diff=False, filter_known_paths=True)
+            with tools.environment_append(tmp):
+                self.assertNotIn("custom_path", os.environ["PATH"])
+                self.assertIn("WindowsFake",  os.environ["PATH"])
+            tmp = tools.vcvars_dict(settings, only_diff=False, filter_known_paths=False)
+            with tools.environment_append(tmp):
+                self.assertIn("custom_path", os.environ["PATH"])
+                self.assertIn("WindowsFake", os.environ["PATH"])
+
     @unittest.skipUnless(platform.system() == "Windows", "Requires Windows")
     def vcvars_amd64_32_cross_building_support_test(self):
         # amd64_x86 crossbuilder